Methods of Using Multilayer Medical Sponges

ABSTRACT

A method of protecting sensitive tissue from damage during a surgical procedure using at least one medical tool having a rotatable bit capable of removing tissue, including selecting a multilayer sponge having (i) a tissue-compatible layer with a tissue contact surface capable of being placed against the sensitive tissue, and (ii) a low-friction layer having a lower coefficient of friction than that of the tissue-compatible layer, being affixed to the tissue-compatible layer, and having an outward-facing surface including biocompatible material not easily worn away by brief contact with the rotatable bit during the surgical procedure. The method further includes placing the tissue contact surface of the biocompatible layer against sensitive tissue such that the outward-facing surface of the low-friction layer is positioned between the sensitive tissue and the rotatable bit to protect the sensitive tissue from damage and prevent the sponge from being drawn around the bit when it rotates.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 12/949,761 filed Nov. 18, 2010 and also claims thebenefit of U.S. Provisional Application No. 61/394,320 filed Oct. 18,2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to protecting sensitive tissue fromrotating instruments and more particularly to using medical sponges thatare constructed with multiple layers.

2. Description of Related Art

Many medical procedures, including surgeries, are performed with the aidof rotating instruments such as drills and burrs. Frequently, drillingor grinding is conducted in close proximity to critical soft tissues,such as brain, blood vessels, and nerves. Working space in thesesurgeries is sometimes limited and may lead to accidental injuries. Forexample, a spinning drill bit removing bone may nick adjacent criticalsoft tissue, causing a potentially serious injury.

Techniques have been developed to protect against these hazards. Theseinclude placing medical sponges on top of critical structures. Spongesnot only help to protect critical tissues, but they also help tomaintain hydration during long operations.

The inventor has recognized that conventional medical sponges sometimesfall short in performing their protective functions. For example,spinning bits present a potential hazard. As is known, drill and grinderbits used in medical procedures may be composed of fluted metal or othermaterials, and may have roughened or abrasive surfaces. Some includeabrasive particles such as diamond burr. All of these various drillingand grinding tools are collectively referred to herein as “bits.” If aspinning bit accidentally touches a sponge, it may “catch” on thesponge, causing the sponge to become dislodged from its protectiveposition and exposing the underlying tissues to damage. Certain bitsintended for cranial, orthopedic and/or dental surgery typically rotateat 75,000 to 85,000 RPM (revolutions per minute). In some cases, thesponge may be caused to wrap around the drill bit and form a fastspinning ball of material. The size and speed of the spinning materialmay be enough to damage adjacent tissues.

BRIEF SUMMARY OF THE INVENTION

The inventor has recognized and appreciated that the safety of surgeriesand other medical procedures may be improved by using a novel multilayermedical sponge. In accordance with one embodiment, the multilayermedical sponge includes at least two layers, a tissue-compatible layerand a low-friction layer. The tissue-compatible layer preferably isabsorbent and is placed against sensitive tissues to cover them andprovide hydration during medical procedures, whereas the low-frictionlayer faces away from these tissues to help protect them from damageresulting from various hazards, such as impingement of medical tools,including spinning drill or grinder bits, upon the multilayer sponge.

This invention features a method of protecting sensitive tissue fromdamage during a surgical procedure using at least one medical toolhaving a rotatable bit capable of removing tissue, including selecting amultilayer sponge having (i) a tissue-compatible layer with a tissuecontact surface capable of being placed against the sensitive tissue,and (ii) a low-friction layer having a lower coefficient of frictionthan that of the tissue-compatible layer, being affixed to thetissue-compatible layer, and having an outward-facing surface includingbiocompatible material not easily worn away by brief contact with therotatable bit during the surgical procedure. The method further includesplacing the tissue contact surface of the biocompatible layer againstsensitive tissue, especially sub-dermal tissue such as brain tissue,such that the outward-facing surface of the low-friction layer ispositioned between the sensitive tissue and the rotatable bit to protectthe sensitive tissue from damage and prevent the sponge from being drawnaround the bit when it rotates.

In accordance with another embodiment, the multilayer sponge includes anabsorbent tissue-compatible layer and a low-friction layer adjacent tothe absorbent layer. Each layer has a surface facing outward. Theoutward-facing surface of the low-friction layer is substantiallysmoother than that of the absorbent layer. Preferably, the low-frictionlayer is visibly smooth and substantially free of fibers, morepreferably completely free of fibers, while the tissue-compatible layerhas a visibly perceptible texture. In some embodiments, thetissue-compatible layer includes fibrous material and protects thesensitive tissue from desiccation. In certain embodiments, thetissue-compatible layer is capable of providing hydration to thesensitive tissue during the surgical procedure.

In accordance with yet another embodiment, the low-friction layer issemi-rigid such that the sponge transitions from stiffness toflexibility with a transition radius of curvature of at least twice theradius of a bit selected for the surgical procedure. In someembodiments, the transition radius of curvature is about two mm to aboutone cm. In certain embodiments, the low-friction layer has a meltingtemperature greater than 300 degrees Celsius.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a perspective view of an exemplary multilayer medical sponge;

FIG. 2 is a side view of the exemplary multilayer medical sponge of FIG.1;

FIG. 3A is a simplified view of an exemplary medical procedure whereinthe multilayer medical sponge of FIGS. 1-2 is placed over sensitivebrain tissue;

FIG. 3B is an enlarged view similar to FIG. 3A showing the radius ofcurvature of the sponge relative to the radius of the bit; and

FIG. 4A is a simplified view of a bit placed against a multilayer spongehaving a transition radius of curvature at least twice the radius of thebit while FIG. 4B is a similar view showing a multilayer sponge have atransition radius of curvature less than twice the bit radius.

DETAILED DESCRIPTION OF THE INVENTION

Techniques, including a preferred embodiment of the invention, aredescribed herein-below for providing a multilayer medical sponge to helpprotect medical patients against injuries arising from various hazardssuch as contact with spinning drill bits and other tools or instruments.These techniques may be employed to make a multilayer medical sponge andto use a multilayer medical sponge to improve the safety of medicalprocedures.

This invention may be accomplished by protecting sensitive tissue,especially sub-dermal tissue such as brain tissue, from damage during asurgical procedure using at least one medical tool having a rotatablebit capable of removing tissue, including selecting a multilayer spongehaving (i) a tissue-compatible layer with a tissue contact surfacecapable of being placed against the sensitive tissue, and (ii) alow-friction layer having a lower coefficient of friction than that ofthe tissue-compatible layer, being affixed to the tissue-compatiblelayer, and outward-facing surface, and including biocompatible materialnot easily worn away by brief contact with the rotatable bit during thesurgical procedure. The method further includes placing the tissuecontact surface of the biocompatible layer against the sensitive tissuesuch that the outward-facing surface of the low-friction layer ispositioned between the sensitive tissue and the rotatable bit to protectthe sensitive tissue from damage and prevent the sponge from being drawnaround the bit when it rotates.

Preferably, a surgical sponge utilized according the present inventionhas substantially opposite friction properties between the twofunctional layers. In order to protect the underlying tissue that itlays on from desiccation and to aid surgical exposure, thetissue-compatible layer preferably is absorbent—i.e., capable of waterretention and blood absorption—and relatively high friction so that itwill not slide off the intended tissue location, even with a drill bitspinning at 75,000-85,000 RPM touching the low-friction layer. On theother hand, in order to prevent the sponge from getting caught by thespinning drill bit, the low-friction layer needs to have substantiallylow friction and local rigidity so that the spinning drill bit slidesover the surface of the stationary sponge without snagging or catchingthe sponge. This unique design is accomplished by manufacturing thesponge with opposing friction properties between the tissue-compatiblelayer and the low-friction layer.

An amount of friction is determined by the contact area and the frictioncoefficient of the sponge material. For the tissue-compatible layer tomaximize friction, a relatively large area that is practically allowedby surgery and a biocompatible material with high friction coefficient,like cotton, can be selected. If the material is made with fiber, eitherwoven or non-woven, it may improve resistance. For the low-frictionlayer, a low friction coefficient material is needed, such aspolytetrafluoroethylene (PTFE). Other suitable low-friction materials,preferably biocompatible and sufficiently flexible, include aluminummagnesium boride (BAM) and diamond-like carbon (DLC). At the same time,the contact area between the sponge and the drill bit has to beminimized. That is, the sponge needs to be sufficiently rigid at andnear the contact point with the drill bit so that it will not deformexcessively and then wrap around the bit. If there is too much contact,the friction between the bit and the sponge can draw the sponge aroundthe bit. However, the sponge has to maintain overall flexibility so thatit will easily fit into a restricted and often irregular surgical field,especially during key-hole operations such as through a cranium. Inaddition, the surgeon will move the spinning bit during drilling fromone surgical field to another and the bit-sponge contact point shiftsaround. The sponge has to allow the shifting of the local stiff areaswithout repositioning. Therefore, the sponge needs local stiffnessaround the drill bit while at the same time to be flexible on a largerscale.

FIGS. 1 and 2 show an exemplary multilayer medical sponge 100 whichprovides bit-resistant characteristics. The sponge 100 includes a firstlayer 160 and a second layer 150. The first layer 160 is made of anabsorbent material in this construction and has an outward-facingsurface 162. The second layer 150 is made of a low-friction,bit-resistant material and has an outward-facing surface 152.Optionally, a radiopaque marker 110 is applied to the sponge 100 and astring 120 is attached to the sponge using, for example, stitching 130as shown in schematic cross-section in FIG. 2. The radiopaque marker 110may be imbedded or painted within sponge 100, e.g., between the layers160 and 150, for use in localizing and identifying the sponge 100 withina surgical field using x-rays. The string 120 may be applied in anysuitable way, such as between the layers 160 and 150 or to the top orbottom of the sponge 100. The string 120 may assist in retrieving orrelocating the sponge 100 during a procedure.

The layers 160 and 150 are affixed together; for example, they may bestitched together. Alternatively, they may be affixed by gluing,heating, melting, bonding, or ultrasonic welding, or by using any othersuitable technique. The low-friction layer 150 may be also applied in aliquid or semi-liquid state, such as by rolling or spraying, and thenallowed to dry or cure.

The absorbent tissue-compatible layer 160 preferably is made from asoft, biocompatible, absorbent material that is safe when placed incontact with sensitive tissues and is capable of retaining water formaintaining hydration of those tissues. It is also preferable for thetissue-compatible layer 160 to have a relatively high frictionalengagement with sensitive tissue to minimize slippage. Non-limitingexamples include cotton, gauze, rayon, silk, or polyester. Othermaterials may be used, and such materials are generally fibrous, porous,or both, to promote wicking action and absorption and retention ofbodily fluids.

The low-friction layer 150 provides bit-resistant characteristics. Inthis manner, the low-friction layer 150 preferably is smoother andsubstantially more slippery than the absorbent layer 160. For example,the surface 152 preferably has a lower coefficient of friction withmetal or diamond burr than the surface 162. The increased slipperinessof the low-friction layer 150 may help to prevent the sponge 100 frombeing dislodged by frictional contact with medical tools andinstruments, such as spinning drill bits. The outer surface 152 of thelow-friction layer may be substantially free of loose fibers, gaps, orother structures that are prone to cause entanglement with a spinningdrill bit. More preferably, the outer surface 152 is completely free offibers and other structures which may cause entanglement. Furthermore, asurface made from woven or non-woven fibers tends to have loose orprojecting fibers as manufactured, as packaged and transported, andespecially after placement sub-dermally and repositioning by forceps orother tools. These loose or projecting fibers (from manufacturing,packaging, manipulation before use, and instrumentation) are likely tobe caught by a fast spinning drill bit and increases the chance that thesponge becomes wrapped around the bit, even if the surface has a lowfriction coefficient measured without the fibers loosened. Material witha foam or expanded structure also creates loose fibers, filaments, orchunks. Therefore, the low-friction layer preferably is a polymer withuniform and smooth surface and structure free of loose fibers. Oneexample is a solid and compact PTFE sheet. Nylon fibers, PTFE fibers,and expanded PTFE (with a foam structure) are generally undesirable forlow-friction layers according to the present invention.

The low-friction layer 150 preferably causes the multilayer sponge 100to be semi-rigid. In this context, “semi-rigid” means relativelyflexible for radii of curvature above a certain transition level, butrelatively stiff for radii of curvature below this transition level. Thephrase “radius of curvature” or “radii of curvature” means a dimensionof “curvature, or bending”. As bending is attempted for increasinglysmaller radii, a state will be reached where the sponge transitions fromrelative flexibility to relative stiffness. For example, when a spongeis used next to a drill bit with a diameter of 5 mm, the radius ofcurvature of the sponge preferably is at least 5 mm, that is, at leasttwice the bit radius of 2.5 mm, so that the sponge does not bend in theundesirable manner illustrated in FIG. 4B. In preferred constructions,the diameter of the drill bit is the minimal radius of sponge curvature.Twice the bit radius allows less contact between the bit and the spongesuch as illustrated in FIG. 4A. In this example, the sponge isrelatively stiff below 5 mm, i.e., it resists further bending undernormal contact pressures. But for bending dimensions above 5 mm, thatis, when the radius of attempted curvature is above 5 mm, the sponge isrelatively flexible so it can be curled, twisted, and bent in normal useas long as the radius of attempted curvature is above 5 mm. Drill bitsused for medical purposes typically have diameters in the range between0.5 mm and 8 mm. Because the low-friction layer 150 causes the sponge100 to be stiff on the scale of typical drill bits, the low-frictionlayer helps to prevent the sponge 100 from deforming easily around thedrill bits and thereby being drawn around them to form spinning balls ofmaterial. At the same time, the semi-rigidity of the low-friction layer150 allows the sponge 100 to remain pliable and compliant on largerscales. Therefore, the sponge 100 may still be draped over sensitivetissues and caused to readily conform to their shapes.

The degree of rigidity of the low-friction layer 150 may be varied basedon the intended use, and different sponges 100 may be provided havingdifferent degrees of rigidity. For example, when using a sponge 100 inthe vicinity of small drill bits, e.g., in the 0.8 mm range, a sponge100 may be selected that has a low-friction layer 150 composed and sizedso as to place the transition between stiffness and flexibility at asmaller radius, such as 2 mm. Conversely, when using a sponge 100 in thevicinity of large drill bits, e.g., in the 8 mm range, a differentsponge 100 may be selected that has a low-friction layer 150 composedand sized so as to place the transition between stiffness andflexibility at a larger radius, such as 1 cm. In a very tight space,there is no room for a big drill bit and the sponge with large curvatureradius may be too rigid to be bent to fit within. Therefore, a moreflexible sponge with smaller curvature diameter in conjunction with asmall drill bit is required. Nevertheless, a sponge with a transitionradius of curvature larger than the bit diameter may still work if thereis enough space to place the sponge, i.e., a 5 mm transition curvaturesponge can work with a 3 mm bit. An assortment of sponges 100 havingdifferent transition radii may be provided.

In addition, the whole sponge preferably has enough elasticity to returnto its original shape when external pressure is removed. During surgicaldrilling in tight and narrow spaces, the sponge is deformed into acurvature by the drill bit. The tissue underneath the sponge iscompressed. After the drilling is completed and the bit is removed, thesponge preferably returns to its original shape to relieve theunderlying tissue from compression. A malleable material with memorylike aluminum foil is undesirable for techniques according to thepresent invention. As the drill bit is removed, aluminum foil would tendto maintain curvature that continues to compress underlying sensitivetissue for an extended and unintended period, potentially causing tissueischemia and necrosis.

The low-friction layer 150 may also be tough. By “tough” it is meantthat the low-friction layer 150 may not be easily worn away by briefcontact with spinning drill bits. Once the low-friction layer 150 hasbeen partly or completely worn away by repeated contact with a drillbit, medical personnel may replace the sponge 100 with a new one.

To provide drill-resistance, the low-friction layer 150 may be composedof materials having one or more of the above characteristics, i.e.,smoothness, slipperiness, freedom from loose fibers or gaps,semi-rigidity, or toughness. Possibly suitable materials, depending onthe procedure, include Gore-Tex®, nylon, Silastic®, and Teflon® PTFE.Some materials such as PTFE are more preferred for temperatureresistance as described in more detail below.

The thickness of the low-friction layer 150 depends upon the materialsused and the desired level of semi-rigidity. In one example, thelow-friction layer 150 is made of Teflon PTFE and has a thickness of0.06 mm. Using this material and thickness, a multilayer sponge 100 maybe constructed having an overall dry thickness of 0.8 mm, which isapproximately the same as the thickness of a conventional medicalsponge. Therefore, the sponge 100 provides protective functions that areabsent from conventional sponges without requiring much if anyadditional size or bulkiness. The fact that the sponge 100 may be madeto be no larger than conventional sponges confers a great advantage insurgeries conducted in very small spaces.

When used in a surgical procedure, the multilayer sponge 100 may beinserted into a surgical field and placed against sensitive tissues withthe absorbent layer 160 contacting the sensitive tissues, therebyallowing the absorbent layer 160 to cover and hydrate them. Thelow-friction layer 150 of the multilayer sponge 100 may face outwardly,away from the sensitive tissues. The low-friction layer 150 may therebyform a protective shield over the sensitive tissues to help guard themagainst intra-operative injury.

FIG. 3A shows an example of a surgical procedure in which a multilayersponge 100 may be employed to help to protect against damage from asurgical tool 330 having a rotatable drill bit 332. The sponge 100 maybe inserted into a surgical field and placed directly over sensitivetissue, such as brain tissue 310. The sponge 100 may be placed with itsabsorbent layer 160 facing toward the brain tissue 310 and itslow-friction layer 150 facing away from the brain tissue 310. Thesurgical procedure may require that certain portions of bone, such asskull bone tissue 340, located close to the brain tissue 310, be removedusing the drill bit 332. With conventional sponges, this procedure maypose a risk that inadvertent contact between the spinning drill bit 332and a conventional sponge would dislodge the sponge from its protectiveposition and possibly cause the sponge to wrap around the drill bit 332and form a dangerously spinning ball of material. However, with themultilayer sponge 100, this risk is significantly reduced. The tough,slippery, and/or semi-rigid qualities of the low-friction layer 150 ofthe multilayer sponge 100 enable it simply to yield to contact with thespinning drill bit 332 without becoming dislodged. Typically, thefrictional forces between the absorbent layer 150 and the underlyingtissue 310 are relatively high, especially when the absorbent layer 150is wet, compared to the frictional forces between the drill bit 332 andthe low-friction layer 150. Consequently, the sponge 100 tends to remainin place. Also, the semi-rigid quality of the low-friction layer 150typically prevents the sponge 100 from deforming around the spinningdrill bit 332 and becoming entangled.

Contact between the spinning drill bit 332 and the sponge 100 may causelocalized heating within the sponge 100. During heavy surgical uses whenthe bit grinds the bone and slides on the resistant layer for a longperiod of time, it may generate intense heat above 300 degrees Celsiusat the contact point between the drill and the low-friction layer,especially with diamond bits. It is preferable for the low-frictionlayer to have a melting temperature above 300 Celsius to prevent thelow-friction layer from melting and thus failing. The tissue-compatiblelayer can prevent heat injury to underneath tissue by insulation and byheat transfer to water which it is saturated with, as long as thelow-friction layer stay in place. PTFE has a melting point of 327Celsius and is suitable for this purpose. Solid nylon with a meltingpoint of 256 Celsius, polyethylene with a melting point of 130 Celsius,polyvinyl chloride with a melting point below 260 Celsius are generallyundesirable for sponges utilized according to the present invention.Further, the sponge preferably is free of chemicals, dye, or drugs thatmay decompose or are unstable above body temperature. If there are drugsadded to the sponge, their release to the body should not be affected bybody fluids, irrigation, and temperature. However, the degree of heatingis much less than with conventional sponges due to slipperiness of thelow-friction layer 150. Also, since the low-friction layer 150 isadjacent to and generally in direct contact with the wet absorbent layer160, heat is quickly drawn away from the point of contact and dispersed,posing little risk of harm. If a medical procedure results in repeatedor frequent contact between the drill bit 332 and the sponge 100,medical personnel may be well advised to replace the sponge 100, or atleast to inspect the low-friction layer 150 for signs of wear beforeexposing the sponge 100 to additional contact with the drill bit. It isunderstood, therefore, that the bit-resistant quality of thelow-friction layer 150 is not intended to be absolute but ratherrelative and significantly improved as compared with that ofconventional sponges.

FIG. 3B provides a schematic cross-sectional view of a rotatable bit 332b having a radius R engaging bone 340 b while pressing against sponge100 b above tissue 310 b.

A bit 432 is shown in cross-section in FIGS. 4A and 4B relative tosponges 400 a and 400 b, respectively, with bone and sensitive tissueomitted for ease of illustration. The transition radius of curvature ofsponge 400 a is greater than twice the radius R of bit 432 and thus issuitably matched for procedures according to the present invention. Incontrast, sponge 400 b has a transition radius of curvature less thantwice radius R and is prone to bit 432 being pressed more than half wayinto sponge 400 b as illustrated in FIG. 4B. Sponge 400 b therefore isgenerally unsuitable for use with bit 432.

The materials used to construct the multilayer sponges 100, 100 a, 400a, and 400 b are preferably biocompatible, non-toxic and free of anysubstances that may cause negative tissue reactions. When the spongesare used in the proximity of spinning drill bits, it is expected that asmall volume of fine debris may be ejected from the sponges. Some ofthis fine debris may remain in the patient's body after surgery.Therefore, it is important to the long-term health of patients that thematerials of the sponges elicit no ill effects, either in the short termor in the long term.

Preferably, the multilayer medical sponges 100, 100 a, 400 a, and 400 bare provided in a range of sizes and shapes, as desired for differentmedical uses. Typically, sponges are rectangular and range in size from0.5 cm by 1 cm to 2 cm by 10 cm, although these are merely examples.Sponges may be provided in any suitable size and shape.

Having described certain embodiments, numerous other embodiments orvariations can be made. For example, the low-friction layers of themultilayer sponges 100, 100 a, 400 a and 400 b may be both bit-resistantand laser-reflective. Also, the low-friction layers of the variousmultilayer sponges may be resistant to other potentially harmful agentsbesides drill bits and laser light. For example, they may protectagainst contact with medical tools such as scalpels and probes. Inaddition, the low-friction layers of the various sponges may help toprotect or shield against debris such as bone chips produced by saws,drills, or other equipment. The same characteristics that allow themultilayer sponges to be bit-resistant may also provide protectionagainst other potentially harmful agents.

As shown and described, the layers and sublayers of each of themultilayer sponges 100, 100 a, 400 a, and 400 b are aligned with otherlayers of the respective sponges and have the same perimeters and areas.This is merely an example. Alternatively, one layer may be made to beintentionally larger or smaller than another layer. For instance, thelow-friction layers may be made to overhang the edges of the absorbentlayers to help protect the edges of the absorbent layers from drills,laser light, and/or other potentially harmful agents. Also, theabsorbent layers 160 may be made to extend beyond the boundaries of therespective low-friction layers to allow for increased fluid absorptionor other benefits.

One may surmise that the low-friction layers are non-porous andimpermeable. Although this may be the case in some instances, it is notrequired. For example, the low-friction layers may be composed of porousmaterials, or they may be perforated to allow them to “breathe” andexchange gases with their surroundings. Any pores or perforations inbit-resistant layers may be much smaller than the diameters of the drillbits with which the sponges are used, to prevent the drill bits from“catching” on the pores or perforations. Also, although the sponges aredescribed in connection with certain surgeries, they may be used in anymedical procedure that employs sponges.

Also, it is understood that the layers of material need not be made fromsolid sheets. For example, the material used to form the low-frictionlayer may be sprayed, rolled, painted, powder coated, or evaporated ontoan absorbent layer, or it may be applied in some other way. Also, thelow-friction layer may be provided as a sticky liquid sheet. Theabsorbent material may then be applied to the low-friction layer as asolid sheet or blown on as loose particles that adhere to thelow-friction layer.

Further, it is not strictly required that the different layers orsublayers be formed from different materials. For example, they may beformed from a single material that is treated differently on itsopposing surfaces. For instance, a material such as polyester may beprovided in the form of a fibrous sheet. During fabrication, one side ofthe sheet could be kept cool while the other side is heated. The heatedside could be allowed to melt to form a smooth, slippery surface, whilethe cool side is maintained in a cool state to remain fibrous andabsorbent.

Although certain embodiments are disclosed herein, it is understood thatthese are provided by way of example only and the invention is notlimited to these particular embodiments. Those skilled in the art willtherefore understand that various changes in form and detail may be madeto the embodiments disclosed herein without departing from the scope ofthe invention.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing. The invention istherefore not limited in its application to the details and arrangementof components set forth in the foregoing description or illustrated inthe drawings. For example, aspects described in one embodiment may becombined in any manner with aspects described in other embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish claim elements.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

1. A method of protecting sensitive tissue from damage during a surgicalprocedure using at least one medical tool having a rotatable bit capableof removing tissue, comprising: selecting a multilayer sponge having (i)a tissue-compatible layer with a tissue contact surface capable of beingplaced against the sensitive tissue, and (ii) a low-friction layerhaving a lower coefficient of friction than that of thetissue-compatible layer, being affixed to the tissue-compatible layer,and having an outward-facing surface including biocompatible materialnot easily worn away by brief contact with the rotatable bit during thesurgical procedure; and placing the tissue contact surface of thebiocompatible layer against the sensitive tissue such that theoutward-facing surface of the low-friction layer is positioned betweenthe sensitive tissue and the rotatable bit to protect the sensitivetissue from damage and prevent the sponge from being drawn around thebit when it rotates.
 2. The method of claim 1 wherein the low-frictionlayer is semi-rigid such that the sponge transitions from stiffness toflexibility at a transition radius of curvature of about two mm to aboutone cm.
 3. The method of claim 1 wherein the low-friction layer has amelting temperature greater than 300 degrees Celsius.
 4. The method ofclaim 1 wherein the low-friction layer includes polytetrafluoroethylene.5. The method of claim 1 wherein the outward-facing surface of thelow-friction layer is visibly smooth and substantially free of fiber. 6.The method of claim 1 wherein the tissue contact surface of thetissue-compatible layer has a visibly perceptible texture.
 7. The methodof claim 6 wherein the tissue contact surface includes fibrous material.8. The method of claim 1 wherein the tissue-compatible layer isabsorbent and protects the sensitive tissue from desiccation.
 9. Themethod of claim 8 wherein the tissue-compatible layer is capable ofproviding hydration to the sensitive tissue during the surgicalprocedure.
 10. A method of protecting sensitive sub-dermal tissue fromdamage during a surgical procedure using at least one medical tool todrive a rotatable bit capable of removing tissue, comprising: selectinga rotatable bit having a first radius for a tissue engagement surface;selecting a multilayer sponge having (i) a tissue-compatible layerincluding absorbent material with a tissue contact surface capable ofbeing placed against the sensitive tissue, and (ii) a low-friction layerhaving a lower coefficient of friction than that of thetissue-compatible layer, being affixed to the tissue-compatible layer,having an outward-facing surface including biocompatible material noteasily worn away by brief contact with the rotatable bit during thesurgical procedure, and being semi-rigid such that the spongetransitions from stiffness to flexibility at a transition radius ofcurvature of at least twice the first radius; and placing the tissuecontact surface of the biocompatible layer against the sensitive tissuesuch that the outward-facing surface of the low-friction layer ispositioned between the sensitive tissue and the rotatable bit to protectthe sensitive tissue from damage.
 11. The method of claim 10 wherein thelow-friction layer has a melting temperature greater than 300 degreesCelsius.
 12. The method of claim 11 wherein the low-friction layerincludes polytetrafluoroethylene.
 13. The method of claim 10 wherein theoutward-facing surface of the low-friction layer is visibly smooth andsubstantially free of fiber.
 14. The method of claim 10 wherein thetissue contact surface of the tissue-compatible layer has a visiblyperceptible texture.
 15. The method of claim 14 wherein the tissuecontact surface includes fibrous material.
 16. The method of claim 11wherein the tissue-compatible layer protects the sensitive tissue fromdesiccation.
 17. The method of claim 16 wherein the tissue-compatiblelayer is capable of providing hydration to the sensitive tissue duringthe surgical procedure.
 18. A method of protecting sensitive braintissue from damage during a surgical procedure using at least onemedical tool to drive a rotatable bit having a first radius for a tissueengagement surface capable of removing bone tissue, comprising:accessing the sensitive brain tissue during the surgical procedure;selecting a multilayer sponge having (i) a tissue-compatible layerincluding absorbent, fibrous material with a tissue contact surfacecapable of being placed against the sensitive tissue, and (ii) alow-friction layer having a lower coefficient of friction than that ofthe tissue-compatible layer, being affixed to the tissue-compatiblelayer, having an outward-facing surface that is visibly smooth andincludes biocompatible material not easily worn away by brief contactwith the rotatable bit during the surgical procedure, having a meltingtemperature greater than 300 degrees Celsius, and being semi-rigid suchthat the sponge transitions from stiffness to flexibility at atransition radius of curvature of at least twice the first radius; andplacing the tissue contact surface of the biocompatible layer againstthe sensitive tissue such that the outward-facing surface of thelow-friction layer is positioned between the sensitive tissue and therotatable bit to protect the sensitive tissue from damage.
 19. Themethod of claim 18 wherein the transition radius of curvature is abouttwo mm to about one cm.